Non-linear pressure development during velocity controlled volume releases in isolated contracting rabbit left ventricle.

Pressure responses obtained during steady-volume releases performed on isolated contracting rabbit left ventricle reveal a typical non-linear time course, dependent on velocity of volume release (VVR) and on amplitude of volume release (AVR). For values of VVR = 4.8 ml/s and of AVR = 0.28 ml (about 20% of the EDV at preload 0.5 kPa) a shoulder shaped pressure-time course is observed. The shoulder is seen during releases independently of the time during systole at which the release starts. When releases are compared which start at the same time during systole but have different velocities then the shoulder appears at higher amplitudes for the higher velocities. The shoulder can be explained by an active actin-myosin interaction within the scheme of a multi-state contraction model.